1. Field of the Invention
The present invention generally relates to an oil tank for an engine-driven vehicle that separates oil from blow-by gas. More particular, the present invention relates to such an oil tank in which blow-by gas is separated from the oil by centrifugal action.
2. Description of the Related Art
In oil tanks, such as that disclosed in United States Published Patent Application No. 2003/0045187, published on Mar. 6, 2003, which claimed priority to Japanese Patent Application No. 2001-233362, filed on Aug. 1, 2001, there often is a mixture of oil and so-called blow-by gases. The oil tank disclosed in the '187 publication comprises an outer cylinder that extends in a vertical direction. An upper cover and a lower cover close off the top and the bottom of the outer cylinder. An inner cylinder is positioned along the axial centerline of the outer cylinder. A plurality of annular partition plates are positioned along the inner cylinder and extend between the inner cylinder and the outer cylinder. These partition plates divide the annular space between the inner cylinder and the outer cylinder into multiple oil chambers in the vertical direction. The inner peripheral edges of the partition plates are fixed to the outer peripheral surface of the inner cylinder while the outer peripheral edges of the partition plates are spaced from the inner peripheral surface of the outer cylinder.
The inlet of the oil tank is in the upper end of the outer cylinder. The inlet is positioned such that the oil flows into the annular space between the outer cylinder and the inner cylinder. The oil inlet also is positioned such that, when seen in plan view, the oil flows in along the inner peripheral surface of the inner peripheral wall of the outer cylinder. The oil outlet of the tank is formed at the lower end of the outer cylinder such that it opens to the lower end of the annular space defined between the inner and outer cylinders.
The annular space is partitioned by the plural partition plates into plural oil chambers arranged in the vertical direction. The oil chambers are connected by the gap formed between the inner peripheral surface of the outer cylinder and the outer peripheral edges of the partition plates. The upper portion of the uppermost oil chamber of the plural oil chambers is connected to the atmosphere by a blow-by gas discharge pipe. One end of the blow-by gas discharge pipe opens to the upper end portion of the annular space and the pipe then extends through the inside cylinder such that the other end is positioned outside of the oil tank.
In an oil tank constructed in this manner, oil mixed with blow-by gas is pressure-fed into the uppermost annular oil chamber. The mixed oil flows along the inner peripheral surface of the outer cylinder and it spins around inside the oil chamber. The oil and the blow-by gas are separated with the oil going to the outer side and blow-by gas moving to a more central location due to centrifugal forces. The spinning of the oil causes these forces and the differences of the specific gravities of oil and blow-by gas causes the movement. The oil flows down into the lower oil chamber through the gap formed between the outer cylinder and the partition plates, and is discharged to the outside of the oil tank (is supplied to the engine) from an oil discharge port positioned in the lowermost portion of the oil tank. The blow-by gas is dispersed into the atmosphere through the blow-by gas discharge pipe from the uppermost oil chamber inside the oil tank.
Because the oil must flow downward through the gaps formed between the outer cylinder and each of the partition plates, and there has been a limit on increasing the flow volume of oil through the tank. For this reason, it has not been possible to use such an oil tank in an engine requiring a large supply of oil.
Sometimes the conventional oil tank cannot separate the blow-by gas from the oil in the upper oil chamber, and blow-by gas remains in the oil. The blow-by gas cannot rise counter to the oil flowing downward. For this reason, the ability of the conventional oil tank to separate gas and liquid is poor and some of the blow-by gas ends up being supplied to the engine together with the oil.
The conventional oil tank has also had the problem that oil mist floating above the liquid surface in the uppermost oil chamber also ends up being discharged into the atmosphere through the discharge pipe together with the blow-by gas.